There are nowadays more and more products that compete with the old-fashioned mop and bucket. Many companies see possibilities to gain a piece of this huge market for wet floor/surface cleaning. In general, these products can be divided in three groups: the bucket and mops (with and without wringers), pre-wetted cloths or so called “quickie wiper” (non-woven cloths like Swiffer wet), and electrically driven floor scrubbers.
What these products have in common is that they all wet the floor with a certain amount of liquid. Wetting the floor is needed for removing the stains from the floor but it also gives a kind of shininess to the floor. This is the main feedback for the consumers that the floor is well cleaned. The amount of water is critical for the key performance indicators: cleaning performance, shininess, drying time and floor damage.
A main disadvantage of the bucket and mop principle is that the amount of water on the floor is difficult to control. It strongly depends on how well the mop is wrung. Some buckets have a mechanical system that helps to wring the mop. Still the amount of water on the floor depends on the force the consumer puts on the wringer and also depends on the amount of force that is put on the mop by the consumer during cleaning the floor. This can result in a poor cleaning performance when the mop is too dry but even worse, it can result in damage to the floor when the mop is too wet.
Pre-wetted cloths do solve this problem but another, maybe even bigger problem occurs. Due to the fact that the pre-wetted cloths can only contain a very little amount of water, the surface area that can be cleaned is very limited, the cloth is drying out too fast. This is also the biggest complaint of the consumer who buys these products. There are several products in the market that try to solve this issue by adding a reservoir and a spray nozzle to the appliance. In this case the user can spray a certain amount of liquid to the floor when he notices that the cloth is too dry. Whether this solution is sufficient depends again strongly on the user. Another disadvantage is that it is not a continuous operating system. The trigger for using it is when the performance is already low. Concluding: all manually operated devices have a high variation in wetness on the floor.
Electric driven floor scrubbers mainly use electric pumps or dosing systems. Apart from the fact that this solution is rather expensive, these systems are very vulnerable for pollution/clogging and in common these pumps are not chemical resistant which is a big issue when detergents are being used. Most pumps use electric power and therefore apart from interfaces to reservoirs and water distributing provisions they need an interface to the electric circuit.
Efforts have also been made to supply sponge mops continuously and evenly with liquids by providing a dosing mechanism, in many cases having a plurality of substantially evenly spaced openings which feed fluid into the sponge. The two primary disadvantages are that these substantially evenly spaced openings become clogged with dirt or other residue and that due to the fact that the amount of liquid which is needed to wet the floor is very limited (1˜6 g/m2), it is very difficult to control the liquid emission, taking the different operating speeds of the device into account.
An in-depth analysis of detergents shows that many detergents react with the calcium in the water and will form a so called soap scum. Soap scum are small particles in the range of 5˜30 micron that float in the water. Those particles can easily block small holes/pores/openings in the liquid dosing mechanism. Test shows that holes larger than 0.3 mm no longer clog due to residue or soap scum in normal daily use.
Test shows that a normal flat mop leaves approximately 3˜6 g liquid on 1 m2 floor at a normal working speed of 5˜10 m2 per minute. That means on average a water flow of 35 ml/min.
To define the size of the opening for the liquid to flow, a simple calculation shows that with an open reservoir filled with a 5 cm water column height and just 1 hole, the diameter should be ˜1 mm (Q=A sqrt ((g*h)/K)). In this formula, Q is flow, A is area of the opening, g is gravity, h is height of the water column, and K is a resistance constant. This formula was used and values were substituted to show the correlation among the above mentioned parameters.
To have an evenly distribution of the liquid on to the mop, just 1 hole is not sufficient. It is obvious that for the number of holes, the more the better counts. But this also means that the diameter of the holes needs to get smaller to get the same flow.
If holes of 0.3 mm are used (good diameter to prevent clogging in normal daily use), just 10 holes can be used to wet the pad. This will not give an evenly distributed water film on the floor.
For a small mop with a width of 250 mm and the holes spaced apart at 5 mm, it means 45 holes are needed. For the same flow of 35 ml/min with 45 holes we need holes of 0.15 mm. Such holes are too small to prevent clogging.
Another disadvantage of such a system is that the water flow strongly depends on the water column height in the reservoir (see above equation). This means that the user has more water on the floor with a just filled appliance and less water after several minutes of use. If also the difference in working speed of the user is taken into account which means if user moves half the speed the appliance gives double amount of water on the floor, it shows that the appliance is not robust and delivers an unpredictable result.
There are systems that make use of a wick e.g. iRobot. All wick systems have a generic disadvantage. The liquid transport makes use of the capillary force of a wick type material (e.g. cotton or microfiber). The capillary force exists due to small pores in the wick material. One end of the wick is in contact with the liquid in the reservoir and is placed inside the reservoir partially whereas the other end is outside the reservoir and is placed in contact with a mopping cloth to transfer the cleaning liquid. As explained above, small pores will clog due to detergents and or soap scum. This means that the lifetime of such element is rather short. Some products try to overcome this problem by selling separate wicks which can be replaced by consumers. It is obvious that this is not ideal, especially when multiple wicks are used to get an even distribution of the liquid to the cloth.